The present invention relates to a device for monitoring a measuring system of an electric drive according to the definition of the species of the independent claim. German Patent 43 30 823 C2 describes a drive device having a safety device for special operation. In a special mode, a redundant safety device monitors the rotation speed of the motor to determine whether it is maintaining a preset maximum, interrupting the power supply to the motor when the rotation speed exceeds the preset maximum. To determine the rotation speed, two different signals are obtained, the first signal being obtained from a rotation speed sensor and the second signal being derived from the variation over time of the current measured by another sensor for this purpose in at least one phase lead to the motor. If the rotation speed detected exceeds a predetermined maximum, the power supply to the motor is interrupted by switching a circuit breaker upstream from a line rectifier and also disconnecting the power inverter. Monitoring a speed sensor on the basis of the current variation is load-dependent and therefore relatively inaccurate. The object of the present invention is to provide an improved monitoring system over the entire rotation speed range without requiring an additional rotation speed sensor.
The device according to the present invention for monitoring a measuring system of an electric drive includes at least one measuring system for detecting a measured quantity of an electric drive and at least one controller which receives at least the measured quantity detected by the measuring system and generates at least one manipulated variable to control the drive. At least one signal processor is provided for detection of errors in the measuring system. This yields early detection of errors in the drive system if there is an error in the measuring system.
In an expedient refinement, at least one quantity generated by the controller is sent to the signal processor for error detection in the measuring system. No additional signal acquisition is necessary for error detection due to a skillful choice of the controller quantity for analysis. Since the controller is available with the drive system anyway, the system""s interference immunity can be improved by simple means.
In an expedient embodiment, the signal processor receives at least one quantity generated by the measuring system and/or derived therefrom for error detection in the measuring system. Including an additional quantity for analysis increases reliability in error detection. If multiple error detection options are provided in particular, analysis of the quantity supplied by the measuring system can be used for checking the plausibility of the error detection.
In another expedient embodiment, a measuring system model that generates at least one estimate expected for the measuring system is provided for error detection in the measuring system. Taking into account the estimate of the measuring system model further increases the reliability of the error detection and can also be used for a plausibility check.
A device according to the present invention for monitoring a measuring system of an electric drive is characterized in that a signal processor generates an error signal, as a function of the synchronous generated voltage, thus indicating an error in the measuring system. The synchronous generated voltage varies when the measuring system of the electric drive, e.g., a rotation speed sensor or a position sensor, slips and therefore there is a sensor offset. In particular, the flux-forming component of the synchronous generated voltage is suitable as a quantity for analysis. The sensor offset with respect to the rotor in comparison with the normal case changes the voltage induced in the field direction and is also available during ongoing operation of the electric drive. Countermeasures can be taken in due time if a faulty sensor arrangement is detected.
In an expedient embodiment, an output quantity of a direct-axis current controller is used to generate an error signal. Usually, to regulate a synchronous or asynchronous machine, a direct-axis current controller is usually provided for regulation of the flux-forming current component. Because of the additional (direct-axis) voltage component induced due to the sensor offset, a system deviation also develops with a direct-axis current controller.
Therefore, the integral component of the direct-axis current controller can be analyzed as a quantity indicating sensor offset in a measuring system, because the integral component is a measure of the additional direct-axis voltage induced due to the sensor offset. This quantity is available at the controller anyway and need not be generated separately.
An advantageous embodiment provides for the quantity indicating sensor offset to be compared with a limit value which depends on the controller parameters and/or the line parameters. System deviations may be caused in particular by the dead time voltage due to the switch dead time of the trigger stage, the induced synchronous generated voltage due to the dead time of the quadrature-axis current controller or parameter deviations in inductors and resistors, additionally affecting the integral component of the direct-axis current controller. Since the controller parameters and line parameters are approximately known, they can be taken into account in selecting the limit value with which the integral component of the direct-axis current controller is compared. This increases accuracy in error detection in the measuring system.
An alternative embodiment is characterized in that the acceleration of the drive derived from the output signal of the measuring system is analyzed. In the subsequent comparison with certain limit values, any lack of mechanical connection between the electric drive and the sensor is detected. In an expedient refinement, this monitoring is active only when the setpoint current preset by the drive controller reaches the maximum allowed setpoint current. In this case, a critical operating situation may be assumed, possibly caused by a defective measuring system. This embodiment is preferably carried out as a plausibility check in parallel with other sensor monitoring methods.
In an alternative embodiment, a rotation speed monitoring model is provided for monitoring a measuring system of an electric drive, generating an estimate of the output signal of the measuring system as a function of certain input quantities. If there arc significant deviations with respect to the actual output signal of that measuring system, a defective measuring system is inferred.
In an expedient embodiment, a selector module is provided to select the monitoring function as a function of the estimated rotation speed. The rotation speed monitoring model is used at high rotation speeds. Since this is ineffective at low rotation speeds, direct-axis voltage monitoring is relied on for this case. This ensures that an error in the measuring system will be detected reliably in any rotation speed range.
Additional expedient embodiments are derived from additional dependent claims and from the description.